I got the lonesome road DLC, and also couriers stash and gunrunners arsenal, when I rebooted it said the level cap was increased by 5.

Fine and dandy.

~But then at a level up I scrolled down the future perks and at the bottom was a perk that requires LEVEL 50 (?)

I thought the base game only went to 28, plus five should have been 33, so what did I add that makes L50 possible?

Or is it possible...

I dunno

it isn't unless you buy all the dlc, personally lonesome road is the last of them to do as it wraps up the story of Ulysses. Each of the four main dlc raises your level cap by 5, lonesome road came out last.